Depends on the thickness of the repair panels as you have a low amp welder,at 2mm 0.8 may be better,0.8mm steel use 0.6mm wire....wait until you get some replies from other landy owners....or buy both in small quantities to try
For what its worth I used 0.8 wire on my Disco and transit van,I find the pinch tension rollers work better on my MiG using 0.8 as those tension rollers have a knurling in the slot and it pushes the wire through better.The weld aint bad either !!
on landy floors I never had a prob with 0.8, I preferred 0.6 but my welder was pretty good at its power distribution. Sills can be better with 0.6 but its expensive.. I would stick with 0.8 especially if your using replacement panels rather than just patching.
I've just finished doing my Discovery. Floor, rear arches, (all patched rather than new panels) new sills made from 100x60x3 RHS, etc, all with 0.6 (as that's what I'd got from years ago) and argon mix on my Portamig.
Just turned it down one notch on really thin stuff.